Webgraphy

About tsunami:
- http://www.angelfire.com/nt/tsunamis
- http://www.drgeorgepc.com/TsunamiImpactSocietySpan.html

About meteor:

- http://en.wikipedia.org/wiki/Meteor
- http://www.meteoritemarket.com/form.htm
- http://www.mira.org/fts0/planets/104/text/txt000x.htm
- http://news.bbc.co.uk/hi/spanish/science/newsid_7007000/7007426.stm
- http://www.solarviews.com/span/meteor.htm

About virus:

- http://en.wikipedia.org/wiki/Virus
- http://en.wikipedia.org/wiki/Introduction_to_viruses
- http://www.dform.com/projects/t4/virus.html
- http://en.wikipedia.org/wiki/Influenza
- http://en.wikipedia.org/wiki/HIV
- http://www.cdc.gov/flu/avian/

About volcano:

- http://www.earthmountainview.com/yellowstone/yellowstone.htm
- http://en.wikipedia.org/wiki/Volcano
- http://www.fun-costa-rica-vacations.com/volcano-vocabulary.html
- http://pubs.usgs.gov/gip/volc/types.html
- http://en.wikipedia.org/wiki/Mount_Pel%C3%A9e
- http://en.wikipedia.org/wiki/Mount_St._Helens

About nuclear energy:

http://www.howstuffworks.com/nuclear-bomb.htm
http://www.atomicarchive.com/Fission/Fission1.shtml
http://hyperphysics.phy-astr.gsu.edu/HBASE/nucene/fusion.html
http://members.tripod.com/~Chernobyl486/index.html
http://en.wikipedia.org/wiki/Nuclear_energy